Add content type prefix to post policy (#1047)

src/main/minio.js

@@ -3665,6 +3665,15 @@ export class PostPolicy {
     this.formData['Content-Type'] = type
   }
 
+  // set Content-Type prefix, i.e image/ allows any image
+  setContentTypeStartsWith(prefix) {
+    if (!prefix) {
+      throw new Error('content-type cannot be null')
+    }
+    this.policy.conditions.push(['starts-with', '$Content-Type', prefix])
+    this.formData['Content-Type'] = prefix
+  }
+
   // set minimum/maximum length of what Content-Length can be.
   setContentLengthRange(min, max) {
     if (min > max) {

src/test/functional/functional-tests.js

@@ -1063,6 +1063,44 @@ describe('functional tests', function () {
       })
     })
 
+    step('presignedPostPolicy(postPolicy, cb)_postPolicy:setContentType', done => {
+      var policy = client.newPostPolicy()
+      policy.setKey(_1byteObjectName)
+      policy.setBucket(bucketName)
+      policy.setContentType('text/plain')
+
+      client.presignedPostPolicy(policy, (e, data) => {
+        if (e) return done(e)
+        var req = superagent.post(data.postURL)
+        _.each(data.formData, (value, key) => req.field(key, value))
+        req.attach('file', Buffer.from([_1byte]), 'test')
+        req.end(function(e) {
+          if (e) return done(e)
+          done()
+        })
+        req.on('error', e => done(e))
+      })
+    })
+
+    step('presignedPostPolicy(postPolicy, cb)_postPolicy:setContentTypeStartsWith', done => {
+      var policy = client.newPostPolicy()
+      policy.setKey(_1byteObjectName)
+      policy.setBucket(bucketName)
+      policy.setContentTypeStartsWith('text/')
+
+      client.presignedPostPolicy(policy, (e, data) => {
+        if (e) return done(e)
+        var req = superagent.post(data.postURL)
+        _.each(data.formData, (value, key) => req.field(key, value))
+        req.attach('file', Buffer.from([_1byte]), 'test')
+        req.end(function(e) {
+          if (e) return done(e)
+          done()
+        })
+        req.on('error', e => done(e))
+      })
+    })
+
     step('presignedPostPolicy(postPolicy)_postPolicy: null_', done => {
       client.presignedPostPolicy(null)
         .then(() => {